Measurements of deposited dose with induced β+ activity in proton and heavy-ion therapy

For the effective utilization of the favorable properties of heavy-ion beams in cancer treatment, it is important to evaluate the range of incident ions and the deposited dose distribution in a patientʹs body. For this purpose, the utilization of positron emitters induced in therapeutic irradiation is, at present, the only feasible method for in situ and non-invasive monitoring of heavy-ion therapy. In this study, we performed irradiation experiments with three species of ions to a water target, and the annihilation gamma-ray distributions were obtained with a positron camera. We applied the maximum likelihood estimation (MLE) method for the detected distributions to derive the range of incident ions and the deposited dose distribution in the target. As a result, the ranges were determined with a difference between the MLE range RMLE and the experimental range Rexp less than 1.1 mm. The good agreement between the estimated dose distribution with the MLE method and the measured one implies that a deposited dose distribution in a target could be estimated from a detected annihilation gamma-ray distribution.